Ischemic strokes are usually caused by a blood clot that blocks or plugs a blood vessel in the brain. This blockage prevents blood from flowing to the brain. Within minutes, brain cells begin to die, which, if not treated rapidly, causes brain damage or death. The costs associated with removing a clot are significant. Most treatments involve thrombectomy: the removal of the clot by aspiration, mechanical retrieval, or some combination thereof.
Removal by aspiration is effected by placing a source of vacuum, e.g., an aspiration or vacuum catheter, upstream of the clot and drawing the clot into or against the distal end of the catheter. Conceptually, aspiration is effective but some significant problems occur in practice. The basic configuration for an aspiration catheter includes a length of hollow catheter having a proximal end fluidically connected to a vacuum or suction pump. In this configuration, operation of the suction pump causes fluid and particulates at the distal end of the catheter to enter the distal opening of the hollow lumen and travel to the proximal end of the lumen near or into the suction pump. Conventional aspiration catheters are threaded through a balloon guide catheter. In one exemplary procedure, the balloon of the guide catheter is guided into the internal carotid artery of the brain. The balloon is inflated to occlude the vessel. The aspiration catheter is threaded through the balloon guide catheter and out the distal end of the guide catheter past the balloon. The distal end of the aspiration catheter is advanced to the clot that is occluding the brain vessel. Suction connected to the aspiration catheter is turned on to cause flow reversal. Ideally, this system aspirates the clot entirely out of the neurovasculature and to the proximal end of the aspiration catheter so that extraction and re-establishment of blood flow could be confirmed. In practice, however, this rarely occurs.
Thrombi are frequently of a larger diameter than the catheter being used to aspirate them. For aspiration to be successful, the thrombus must deform to conform to the inner diameter of the aspiration catheter. During conventional aspirations, it is common for applied vacuum to partially draw a thrombus into the distal opening of the aspiration catheter's lumen, thereby deforming some of the thrombus to the catheter's inner diameter. At this point, the thrombus becomes lodged completely within, partially within, or at the distal opening of the aspiration catheter, a condition that can be referred to as corked or corking. In effect, the distal end becomes a suction cup grasper for the clot. When this situation occurs, a surgeon's only option is to use the aspiration catheter as a fishing line to pull the clot back through the balloon guide and out of body. The other option is not viable, that is, reversing the suction to pressurize the clot and eject it forcibly and uncontrollably out of the distal opening of the aspiration catheter. Such action is dangerous to the patient for many reasons, the primary one being that forcibly and uncontrollably ejecting the clot may cause the clot to move further distally within the vessel in which it was originally lodged. That distal movement would not only cause the clot to be further within the vessel—i.e., in an even smaller diameter of the vessel than when it was originally lodged—but it could permanently lodge the clot into that vessel, making it impossible to remove, or it could burst the vessel. Those of skill in the art know that these situations are to be avoided because of the serious potential risks to the patient.
Even when the surgeon uses the aspiration catheter to fish out the clot, there is no assurance that the entirety of the clot will be removed. Pieces of the clot can break off during movement, when that occurs, the pieces re-embolize within the same vessel or within different vessels that might be even more difficult to remove.
When all or most of the clot is drawn out from the patient, it is difficult to confirm that the entire thrombus was removed. A significant disadvantage of current thrombus removal devices is the inability of a surgeon to ascertain thrombus capture/removal without the full withdrawal of a given therapeutic device from a patient's anatomy. Even systems capable of fully aspirating a given thrombus are problematic, because the reservoirs into which aspirated contents are deposited are located outside of the sterile field in an operating room setting. This location, outside the sterile field, makes it difficult or impossible for physicians operating aspiration catheters to easily visualize and appraise aspirated thrombus material.
To confirm thrombus removal can require the surgeon to attempt aspiration again. The aspiration and balloon guide catheters have to be cleaned out, access to distal anatomy has to be re-established, and, when the aspiration catheter finally is located back at the embolism site, the same issues may be present again with whatever embolus material remains. A disadvantage of these procedures is the significant increase in procedure time, which not only significantly increases the cost (as each minute in an operating room is expensive), it also increases the surgeon's stress, which decreases the success rate of the operation.
First-pass recanalization rate is a metric used to determine the efficacy of thrombectomy systems. Most current systems offer rates of between 30% and 60%. A system that increases the first-pass recanalization rate is valuable and desirable.
Even with an attempt to maintain vacuum pressure utilizing manual periodic cycling, prior art systems are not capable of avoiding positive pressures at the distal end of the catheter. Prior art systems are not able to react quickly enough to keep the distal end of the catheter from experiencing a positive pressure. When positive pressure exists at the distal end of the lumen, liquid from inside the lumen exits out from the distal end of the catheter in a distal direction. This is referred to as forward flow. The prior art do not have a fast enough reaction time to quell forward flow. Forward flow, therefore, can and does remove thrombi off of the distal end and risk sending thrombi further distally in the vasculature. Such systems cannot guarantee removing all forward flow eliminating positive pressure at the distal end of the catheter.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.